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Step-by-step instructions for performing operations with Kubernetes.

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Run a Stateless Application Using a Deployment

This page shows how to run an application using a Kubernetes Deployment object.

Objectives

Before you begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube, or you can use one of these Kubernetes playgrounds:

Creating and exploring an nginx deployment

You can run an application by creating a Kubernetes Deployment object, and you can describe a Deployment in a YAML file. For example, this YAML file describes a Deployment that runs the nginx:1.7.9 Docker image:

deployment.yaml 
apiVersion: apps/v1beta1
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  replicas: 2 # tells deployment to run 2 pods matching the template
  template: # create pods using pod definition in this template
    metadata:
      # unlike pod-nginx.yaml, the name is not included in the meta data as a unique name is
      # generated from the deployment name
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.7.9
        ports:
        - containerPort: 80

  1. Create a Deployment based on the YAML file:

     kubectl create -f https://k8s.io/docs/tasks/run-application/deployment.yaml

  2. Display information about the Deployment:

     kubectl describe deployment nginx-deployment

 user@computer:~/kubernetes.github.io$ kubectl describe deployment nginx-deployment
 Name:     nginx-deployment
 Namespace:    default
 CreationTimestamp:  Tue, 30 Aug 2016 18:11:37 -0700
 Labels:     app=nginx
 Selector:   app=nginx
 Replicas:   2 updated | 2 total | 2 available | 0 unavailable
 StrategyType:   RollingUpdate
 MinReadySeconds:  0
 RollingUpdateStrategy:  1 max unavailable, 1 max surge
 Conditions:
   Type          Status  Reason
   ----          ------  ------
   Available     True    MinimumReplicasAvailable
 OldReplicaSets:   <none>
 NewReplicaSet:    nginx-deployment-1771418926 (2/2 replicas created)
 No events.

  3. List the pods created by the deployment:

     kubectl get pods -l app=nginx

 NAME                                READY     STATUS    RESTARTS   AGE
 nginx-deployment-1771418926-7o5ns   1/1       Running   0          16h
 nginx-deployment-1771418926-r18az   1/1       Running   0          16h

  4. Display information about a pod:

     kubectl describe pod <pod-name>

    where <pod-name> is the name of one of your pods.

Updating the deployment

You can update the deployment by applying a new YAML file. This YAML file specifies that the deployment should be updated to use nginx 1.8.

deployment-update.yaml 
apiVersion: apps/v1beta1
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  replicas: 2
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.8 # Update the version of nginx from 1.7.9 to 1.8
        ports:
        - containerPort: 80

  1. Apply the new YAML file:

     kubectl apply -f https://k8s.io/docs/tutorials/stateless-application/deployment-update.yaml

  2. Watch the deployment create pods with new names and delete the old pods:

     kubectl get pods -l app=nginx

Scaling the application by increasing the replica count

You can increase the number of pods in your Deployment by applying a new YAML file. This YAML file sets replicas to 4, which specifies that the Deployment should have four pods:

deployment-scale.yaml 
apiVersion: apps/v1beta1
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  replicas: 4 # Update the replicas from 2 to 4
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.8
        ports:
        - containerPort: 80

  1. Apply the new YAML file:

     kubectl apply -f https://k8s.io/docs/tutorials/stateless-application/deployment-scale.yaml

  2. Verify that the Deployment has four pods:

     kubectl get pods -l app=nginx

    The output is similar to this:

     NAME                               READY     STATUS    RESTARTS   AGE
 nginx-deployment-148880595-4zdqq   1/1       Running   0          25s
 nginx-deployment-148880595-6zgi1   1/1       Running   0          25s
 nginx-deployment-148880595-fxcez   1/1       Running   0          2m
 nginx-deployment-148880595-rwovn   1/1       Running   0          2m

Deleting a deployment

Delete the deployment by name:

kubectl delete deployment nginx-deployment

ReplicationControllers – the Old Way

The preferred way to create a replicated application is to use a Deployment, which in turn uses a ReplicaSet. Before the Deployment and ReplicaSet were added to Kubernetes, replicated applications were configured by using a ReplicationController.

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